{"id":476,"date":"2008-06-18T00:08:24","date_gmt":"2008-06-18T05:08:24","guid":{"rendered":"http:\/\/arxivblog.com\/?p=476"},"modified":"2008-06-18T00:09:09","modified_gmt":"2008-06-18T05:09:09","slug":"the-embarrassing-lightness-of-photons","status":"publish","type":"post","link":"https:\/\/arxivblog.com\/?p=476","title":{"rendered":"The embarrassing lightness of photons"},"content":{"rendered":"<p><a href=\"http:\/\/arxivblog.com\/wp-content\/uploads\/2008\/06\/photon-force.jpg\" title=\"Photon force\"><img decoding=\"async\" src=\"http:\/\/arxivblog.com\/wp-content\/uploads\/2008\/06\/photon-force.thumbnail.jpg\" alt=\"Photon force\" \/><\/a><\/p>\n<p>Here&#8217;s a conundrum for you. What is the momentum of light in a transparent dielectric medium?<\/p>\n<p>If the answer doesn&#8217;t trip off your tongue, that might be because nobody else knows either. Amazingly, there are two lines of thought:<br \/>\nIn 1908, the German mathematician Hermann Minkowski guessed that the momentum was equal to nE\/c (where n is the refractive index, and E and c are the energy and speed of light in a vacuum).<\/p>\n<p>A year later,\u00a0 his contemporary Max Abraham suggested that the momentum is equal to E\/nc.<\/p>\n<p>A century since then and we&#8217;re none the wiser. An embarrassing state of affairs for theoretical physics, wouldn&#8217;t you agree?<\/p>\n<p>Today Weilong She and pals from Sun Yat-Sen University in Guangzhou, China, announce that they have the answer. And they got it by measuring the recoil on the end face of a nanometre-sized fibre exerted by outgoing light. (This isn&#8217;t the well known pressure caused by specular reflection but something\u00a0 a little more subtle.)<\/p>\n<p>The experiment is impressive because it is designed in such a way that if Minkowski were correct the fibre should be pushed in one direction and in the other if Abraham were correct.<\/p>\n<p>So the result is the first to unambiguously favour one theorist over the other.<\/p>\n<p>And the winner is&#8230;drum roll&#8230;Abraham.<\/p>\n<p>It&#8217;s about time.<br \/>\nRef:\u00a0 <a href=\"http:\/\/arxiv.org\/abs\/0806.2442\">arxiv.org\/abs\/0806.2442<\/a>: Observation of a Push Force on the End Face of a nm Fiber Taper Exerted by Outgoing Light<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Here&#8217;s a conundrum for you. What is the momentum of light in a transparent dielectric medium? If the answer doesn&#8217;t trip off your tongue, that might be because nobody else knows either. Amazingly, there are two lines of thought: In 1908, the German mathematician Hermann Minkowski guessed that the momentum was equal to nE\/c (where [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10,16],"tags":[],"class_list":["post-476","post","type-post","status-publish","format-standard","hentry","category-fightin","category-seein-the-light"],"_links":{"self":[{"href":"https:\/\/arxivblog.com\/index.php?rest_route=\/wp\/v2\/posts\/476","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/arxivblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/arxivblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/arxivblog.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/arxivblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=476"}],"version-history":[{"count":0,"href":"https:\/\/arxivblog.com\/index.php?rest_route=\/wp\/v2\/posts\/476\/revisions"}],"wp:attachment":[{"href":"https:\/\/arxivblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=476"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/arxivblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=476"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/arxivblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=476"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}